How River Blindness is Transmitted

How is river blindness transmitted?

Onchocerciasis is a parasitic disease spread by the bites of black flies, which deposit the larvae of the Onchocerca volvulus worm into the body. The parasites are small, threadlike worms, which live under the skin often in aggregated clumps called nodules. Adult worms live for about seven to 15 years. The female worms produce thousands of offspring called microfilariae. The microfilariae leave the nodules and migrate to the upper layer of the skin, where they can transfer to black flies when the insects bite to take a blood meal. In the fly, the microfilariae develop into infective larvae, which can then be transmitted to the next unknowing victim during the fly's next bite. Over the course of a year, these larvae mature into adult worms, and the cycle continues.

The symptoms caused by river blindness are not related to the adult worms or the fly bites but to the microfilariae, which irritate the skin and cause intense itching, skin discoloration, and rashes.

Unlike infections transmitted by biting insects where one bite is enough to cause serious disease, such as malaria and dengue fever, hundreds of bites are usually required to acquire onchocerciasis.

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